Dogs can be trained to sniff out bowel cancer, even when the disease is in its early stages, researchers in Japan claim.

In a series of experiments that involved sniffing the breath or stool samples of patients, a specially-trained labrador retriever proved nearly as good at identifying those with cancer as a conventional colonoscopy examination.

The team, led by Hideto Sonoda at Fukuoka dental college hospital, said some dogs have such a keen sense of smell that they can detect minute traces of chemicals that appear to circulate in the bodies of people who have cancer.

The finding builds on previous experiments in which researchers used dogs to sniff out cancers in the skin, lungs, bladder and ovaries.